Abstract

A previous application of the advanced diagnostic method, Molecular Tagging Velocimetry (MTV), showed promise with respect to providing an improved understanding of velocity fields in the complex thermo-solutal flows associated with solidification in the presence of significant buoyancy. The present study extends the earlier results (Wirtz et al, 1998) in an ammonium-water alloy analog by demonstrating the capability of quantifying two components of the instantaneous velocity vectors of such flows. The model alloy was directionally-solidified by chilling from below. Velocity vectors were measured near the solidification front at early phases (∼3minutes) of the solidification when fine structures exist. Well-defined convective flow patterns were documented with velocities on the order of 1 mm/s measured for both velocity components. Velocity vectors within and around a plume were also measured further away from the solidification front later in the solidification process (∼100 minutes). The optical grid used for tagging must be refined to provide adequate spatial resolution within the plumes. The capabilities and limitations of the MTV method in its present realization are described. The results demonstrate that the MTV method is a powerful tool that can be expected to provide valuable data related to complex thermo-solutal flows associated with solidification in the presence of significant buoyancy.

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